VHF Josephson Arbitrary Waveform Synthesizer

We report on the design, fabrication, and measure-ment of a very high frequency band Josephson arbitrary waveformsynthesizer (VHF-JAWS) at frequencies from 1 kHz to 50.05 MHz.The VHF-JAWS chip is composed of a series array of 12 810Josephsonjunctions(JJs)embeddedinasuperconductingcoplanarwaveguide. Each JJ responds to a pattern of current pulses bycreating a corresponding pattern of voltage pulses, each with atime-integrated area related to fundamental constants ash/2e.Thepulse patterns are chosen to produce quantum-based single-tonevoltage waveforms with an open-circuit voltage of 50 mV rms (-19.03 dBm output power into 50 Omega load impedances) at frequenciesup to 50.05 MHz, which is more than twice the voltage that has beengenerated by previous RF-JAWS designs at 1 GHz. The VHF-JAWSis "quantum-locked," that is, it generates one quantized outputvoltage pulse per input current pulse per JJ while varying the dccurrent through the JJ array by at least 0.4 mA and the amplitudeof the bias pulses by at least 10 %. We use the large bias pulsequantum-locking range to investigate one source of error in detail:the direct feedthrough of the current bias pulses into the DUT atVHF frequencies, which adds an unwanted, in-band componentto the measured voltage. We reduce this error by high-pass filter-ing the current bias pulses and measure the error as a functionof input pulse amplitude using two techniques: 1) by measuringsmall changes over the quantum-locking range and 2) by passivelyattenuating the input pulse amplitude so that the nonlinear JJsno longer generate voltage pulses while the error is only linearlyscaled.